Apparatus for preparing airfelt

ABSTRACT

Apparatus and process for continuously converting dried cellulosic fibrous sheet material into a dispersion of individual fibers in air and thereafter forming said individual fibers into an airfelt.

United States Patent 1' Buell [111 3,824,652 July 23, 1974 APPARATUS FORPREPARING AIRFELT [75] Inventor: Kenneth B. Buell, Cincinnati, Ohio [73]Assignee: The Proctor & Gamble Company, Cincinnati, Ohio 22 Filed: June22, 1973' 21 Appl. No.: 372,729

Related US. Application Data [62] Division of Ser. No. 182,795, Sept.22, 1971.

[52] US. Cl. 19/1563, 19/83 [51] Int. Cl D01g 25/00 [58] FieldofSearch..19/83,88,89,l55,

[56] References Cited UNITED STATES PATENTS 3,606,175 9/1971 Appel etall 19/1563 X 3,637,146 1/1972 Banks 19/1563 X 3,692,622 9/1972 Dunning19/1563 X FOREIGN PATENTS OR APPLICATIONS 1,415,428 9/1965 France 19/831,010,147 11/1965 Great Britain 19/156 X Primary Examiner-Dorsey NewtonAttorney, Agent, or Firm-Elliot A. Lackenbach; John V Gorman; Richard C.WittepFrederick H. Braun [5 7] ABSTRACT Apparatus and process forcontinuously converting dried cellulosic fibrous sheet material into adispersion of individual fibers in air and thereafter forming saidindividual fibers into an airfelt.

4 Claims, 8 Drawing Figures PATENTED M2319 snmanrz Fig. 7

Fig.

APPARATUS FOR'PREPARING AIRFELT This is a division of application Ser.No. 182,795, filed Sept. 22, 1971.

FIELD OF THE INVENTION This invention relates to the art ofdisintegrating fibrous sheet material and using the disintegrated material to form an airfelt. More particularly, it relates to apparatuswhereby a dried cellulosic fibrous sheet is impacted under predeterminedoperating conditions to cause progressive disintegration of the sheetinto individual fibers and thereafter distributing said fibers onto aforaminous support toproduce an airfelt.

PRIOR ART A similar process is disclosed in US. Pat. No. 3,519,21 lwhere a disintegration device of the general type utilized herein isdisclosed. This patent also envisions the formation of an airfelt pad.Said patent is incorporated herein by reference.

The present invention differs from the apparatus and process of US. Pat.No. 3,519,211, in one aspect, by providing an air control system whichkeeps individual fibers distributed in a minimum amount of air tominimize the problem of separating the fibers from the associated air.This invention also comprises an improved design and arrangement ofimpacting elements and the provision of means to prevent the buildup offibers in the inlet of the disintegrator. A further aspect of thepresent invention involves control of the fiber density across thedisintegrator discharge outlet so as to produce an airfelt which variesin basis weight across its width in a predetermined manner.

OBJECTS OF THEINVENTION The principal object of the invention is toimprove the operation of prior devices as represented by US. Pat. No.3,519,21 l.

Another object of this invention is to provide apparatus which willdisintegrate fibrous sheet material into its component fibers andthereafter, with a minimum time lag, use said fibers to form an airfelt.

SUMMARY OF THE INVENTION tion of rotation at an angle of from about to'about 40 from the radii drawn through the front edges of the teeth stips and the top surfaces of said teeth being inclined inwardly to forma relief angle of from about to about 60; and

2. a casing for said disintegrating element comprising a support elementfor said fibrous material to continuously hold said fibrous materialwhile it is being fed into a position where said disintegrating elementcan impact the fibrous material to separate said material into itsindividual fibers, the distance between said disintegrating element andsaid support element being from about 0.010 to about 0.080, preferablyfrom about 0.025 in. to about 0.035 in., said casing defining, incooperation with said disintegrating element, a restricted air flowchannel to keep the current of air and entrapped individual fibers,which results from rotating said 5 disintegrating element todisintegrate said fibrous material, within a minimal cross-sectionalarea, said casing having a primary discharge outlet for the air andfiber current, said discharge outlet being tangentially directed withrespect to said disintegrating element, said casing having an air inletimmediately adjacent the said primary discharge outlet and between saidprimary discharge outlet and the point where the fibrous material isimpacted, said casing having secondary air inlets in the casing acrossthe width of said primary discharge outlet; and said casing havingvacuum air outlets in said support element about 1 inch to about 4inches from the point where the disintegrating element impacts saidfibrous materiakand B. A moving foraminous support element across theopening of said discharge outlet adapted to collect the individualfibers to form an-airfelt while permitting the air to escape throughsaid foraminous support element, said foraminous support element beingat a distance from the center of said disintegrating element of fromabout three-fourths to about two diameters of said disintegratingelement but no further than about 3 feet.

THE PROCESS In accordance with another aspect, the present inventioncomprises a process of disintegrating dried cellulosic fibrous sheetmaterial in a process comprising 35 the steps of:

A. Feeding said fibrous sheet into a disintegrator comprising adisintegrating element having a plurality of impacting elements whichhave tips and a casing having a slotted opening terminating in a sheetsupport element, said casing defining, in combination with saiddisintegrating element, arestricted channel;

B. Supporting said sheet in said slotted opening;

C. Moving said disintegrating element such that the tips of saidimpacting elements move at a velocity of at least about 6,000feet/minute;

D. Impacting said tips against the end of said fibrous sheet so thatimpact is subtantially normal to the plane of said sheet whereby saidfibrous sheet is disintegrated into individual fibers;

E. Mixing said fibers with air in said restricted channel with saidimpacting elements s while maintaining a relatively even fiberdensitygradient and air flow velocity gradient across the axial width of saidchannel; and

F. Removing the fiber/air mixture from the disintegrator along a tangentto the direction of motion of said impacting elements at a point ofremoval to a foraminous support positioned no more than about 3 feetaway from said point at which the fiber/air mixture leaves saidimpacting elements, said air passing through said foraminous support andleaving said fibers on said .foraminous support in the fomi of anairfelt.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes withclaims particopment of the periphery of the axial rotary cylindricaldisintegrating element rotatable about its cylindrical axisschematically showing, in flattened form, the tooth tip array;

FIG. 4 is a fragmentary elevational view of the discharge outlet portionof the casing as viewed along line 4-4 of FIG. 1, showing a series ofair inlet ports;

FIG. 5 is a cross-sectional view of the discharge outlet taken alongline 55 of FIG. 1;

FIG. 6 is a transverse cross-sectional view of an airfelt product havinga transversely varying basis weight;

FIG. 7 is a cross-sectional view of the discharge outlet taken along theline 7-7 of FIG. 1; and

FIG. 8 is a fragmentary cross-sectional view of the vacuum ports takenalong the line 88 of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, apreferred'embodiment of the apparatus and process will be described withparticular reference to the disintegration of a dried cellulosic fibroussheet. ln order to simplify the disclosure, elements which form no partof the present invention and which can be readily supplied by persons ofordinary skill in the art have been omitted. Such elements includestructural members, bearings, power transmission arrangements, and thelike.

This invention is particularly useful in disintegrating comminutiongrade wood pulp in dry lap form of the kind found in commerce. Such drylap sheets typically have a basis weight, air-dried, of between about100 and about'200 lbs. per thousand square feet and generally have acaliper of at least about 0.04 in. or greater. A dry lap sheet of thistype usually has a moisture content of about 6 percent. However, sheetshaving lower moisture contents can be used in connection with thepresent invention and, in fact, those having moisture contents of about1 percent have been found to produce excellent results. Sheets havingmoisture contents higher than about l0 percent can be used, but thesemust be disintegrated at lower rates, or they will be incompletelydisintegrated.

As used herein, the term dried cellulosic fibrous sheet describes anytype of fibrous sheet material capable of disintegration by the processof this invention. On the other hand, a dry lap sheet will be understood-to mean a wood-fiber material of the above-described characteristics towhich the invention is preferably applied.

Referring now to FIG. 1, a roll 11 of dry lap material is unrolled intoa sheet 12 which is advanced to the disintegrator 13. The sheet 12 isfed radially into the disintegrator 13 by a pair of counter-rotatingmetering infeed rolls 14 and 15 which are mounted on the infeed side ofthe disintegrator 13. A motive power source, which may typically be anelectric motor, but which preferably is tied to the speed of thesubsequent converting lines main drive to provide exact basis weightcontrol. This motive power source is connected to the infeed rolls 14,15 in a conventional manner (not shown) to provide a driving force.

The disintegrator 13 comprises a casing l6 having a generallycylindrical bore 17. A shaft 18 is journaled in the closed ends of thecasing 16 such that one end of shaft 18 extends outside the casing 16 topermit coupling the shaft in a conventional manner to a motive sourcesuch as an electric motor. The motor continu- ,ously drives the shaft 18in a counter-clockwise direction, as shown.

The casing 16 comprises an inlet portion 19 which is slotted to providean inlet opening having an inner end 19a. The inlet opening receives thedry lap sheet 12 and guides it to the inner end 19a which defines asheet support element or edge portion whereat the dry lap sheet 12 isdisintegrated. The inlet opening is essentially the same size as thesheet 12 with a clearance of from about 0.040 to about 0.200 inch,preferably from about 0.80 to about 0.125 inch, larger clearances beingdesirable along the edges to permit using slightly damaged sheet 12. Arelatively large tangential discharge outlet 20 is provided in thecasing 16 at a point of from about 5 to about 270 from the inlet portion19 in the direction of rotation of shaft 18. FIG. 1 of the drawingshows, in solid lines an approximate 180 separation between the inletportion 19 and the discharge outlet 20 and, in phantom lines, an inletportion .19 providing an approximate 5 separation to the dischargeoutlet 20 and an inlet portion 19" providing an approximate 270separation to the discharge outlet 20. It is to be emphasized that theangle referred to is the angle of separation, i.e., the angle subtendedon the surface of the casing between the slot in the inlet portion andthe edge of the discharge outlet and not the angle between the axis ofthe inlet and discharge openings. Preferably, the discharge outlet 20 issufficiently far from the inlet opening 19 to permit the fibers to becompletely disintegrated before discharge. The discharge outlet 20, incross-section, has a width approximately equal to the length ofcylindrical bore 17 and a depth of from about 2 inches to about 4inches, preferably 3 inches. Air inlet openings 2lare provided near thedischarge outlet 20 to permit air to be forced into the casing 16 at aslight positive pressure from a suitable blower (not shown) or the like,for the purpose of preventing the recycling of the fibers through thedisintegrator 13 and for other purposes disclosed hereinafter.

Suitably, the air inlet opening 21 can be one or more slots from aboutinch to about 1 inch wide running the entire width of the casing 16 nearthe tangential discharge outlet 20. Under a pressure of about 2 to about10 inches of water,'the inlet openings can admit air at a velocity ofabout 6,000 to about 13,000, preferably 8,000 feet per minute.

As shown in FIGS. 1 and 4, additional air inlets 22 are provided for thepurpose of adjusting the air flow in the discharge outlet 20. The airinlets 22 are arranged in a straight line across the discharge outlet 20near the tangential discharge point. In FIG. 4, only a few of the inlets22 are shown, but it is understood that additional inlets 22 areprovided at the indicated points. The inlets 22 are each controlled byvalve means (not shown), for example, cap and seat valves such as thoseused on piccolos and are of a size to deliver air at a velocity of fromabout 6,000 to about 13,000, preferably 8,000 fpm under 2 to inches ofwater pressure.

Rotors 23 are keyed to the shaft 18 in juxtaposed relation, each beingprovided with a plurality of teeth'24 extending outwardly such thattheir tips 25 are adapted to serve as impacting elements. As usedherein, rotor refers to thin rotor discs having widths of from about0.030 to about 0.125 inch. A small clearance of from about 0.023 in. toabout 0.035 in. is preferably provided between the tips 25 and the innerend 19a of the inlet opening in the inlet portion 19 which forms a sheetsupport for the sheet 12, as disclosed in the copending application ofGeorge Morgan entitled DIS- INTEGRATION PROCESS FOR FIBROUS SHEETMATERIAL, now US. Pat. No. 3,750,962 and incorporated herein byreference. Larger and smaller clearances of from about 0.010 to about0.080 in. can be used, depending upon the operating rates, provision ofcooling means, etc.

With the above arrangement of the parts of the apparatus, successiveteeth tips 25 impact the end of the infeeding sheet 12 as the rotors 23are turned. The rotors 23 when keyed in place and bolted together forman axial rotary cylindrical disintegrating element 26 rotatable aboutits cylindrical axis. This configuration is preferred since it permitsthe favorable internal distribution of stresses set up during operationof the disintegrator. The discharge outlet 20 is generally tangentiallypositioned with respect to said disintegrating element 26.

Referring now toFIG. 2, an individual rotor 23 is shown. Each rotor 23desirably bears from about 6 to about 18 teeth 24, preferably about 8teeth 24, equally spaced about its periphery with their tips 25 locatedat like distances from the rotor 23 axis. The impact face 27 of eachtooth 24 isformedat the angle a with the radius of the rotor 23 whichpasses through the tooth tip 25. The top 28 of the tooth 24 is formed ata relief angle ,3, i.e., the angle defined by the top 28 of the tooth 24and a tangent to the rotor 23 passing through the tooth tip 25. Theangle a can vary from about 15 to about 40 and the angle ,8 varies fromabout 20 to about 60. Angle a is the more critical of the two angles.Both larger and smaller angles for angle a give poorer totalfiberization, the larger limit being most critical. Angle B is importantbecause if the top of the tooth 28 is tangential to the rotor 23, or isinclined outward, a splinter-like mass of glassined cellulose will beformed along the top of the tooth 28 during operation which will thenbreak off and be discharged along with the individual fibers out thedischarge outlet 20. The individual rotors 23 are relatively thin,typically being from about 0.030 to about 0.125 in. in width.Accordingly, it is desirable to have blunt projections 29 which willhelp support the teeth 24 of adjacent rotors 23 when, as is preferred,the rotors 23 are bolted together to form said disintegrating element26. For the purpose of bolting the rotors 23 together, a series of holes30 is provided in each rotor 23.

tip 25 is rounded to a 0.030 radius; the radius to the tip of the smallsupport projections is about 5.38 inches and to the tip 25 of teeth 24is about 5.75 inches; and the holeswhich take the bolts are 17/32 inchesin diameter bored on an approximately 4.7525 diameter.

Referring now to FIG. 3, which is a fragmentary plan view of a surfacedevelopment of the periphery of disintegrating element 26, showing inflattened form the locations of tooth tips 25 of the rotors 23, as theyare preferably connected. It can be seen that the tooth tips 25 arearranged in a staggered pattern so that individual tips 25 are not closetogether. If the tooth tips 25 on all the rotors23 were aligned so as tomake solid lines of tooth tips 25, or if one or more of the tips 25 weretoo close together, disintegration quality would be poor. The tendencyin such an aligned arrangement is to tear the fibrous sheet materialinto chunks rather than individual fibers. Also, the noise of thedisintegrating element 26 when it is rotating would resemble a firesiren if the teeth were aligned.

If said disintegrating element 26 had the tips 25 in a completely randomarray, this would be ideal since it is desired to create a design whichwill not cause lateral fiber migration or consistent noise and vibrationreinforcement. However, using individual rotors 23 with the same numberof teeth, in a balanced configuration, a completely random configurationis not feasible. Applicant has found that a reasonable approximation ofrandom distribution can be achieved by arranging the teeth tips 25 in amultiple helical pattern in which there are a plurality of patterns ofteeth 24 on a plurality of portions of the circumference of saiddisintegrating element, each portion covering the entire width of saiddisintegrating element and each portion being paired with acorresponding adjacent portion which is substantially a mirror image ofthe first portion, each portion covering from about 30 to about 45 ofthe cir cumference of the disintegrating element, the helical patternshaving helical angles of from about 10 to about 35, and each tooth 24being arranged so that the nearest teeth 24 in all directions are atapproximately equal distances. Preferably, the mirror image portion isoffset slightly from what would be the exact mirror image position.

One such arrangement of teeth 24 is shown in FIG. 3 where the pattern ofthe teeth tips 25 is shown. Rows l-5 comprise a Set X (i.e., a firstportion bearing a helical pattern) in which succeeding rows of tips 25are offset at a helical angle of from about 10 to about 35 from thepreceding teeth tips 25, i.e., angle y varies from about 10 to about 35.Rows 6-10 comprise Set Y (i.e., a second adjacent portion bearing ahelical pattern which is an approximate mirror image of the pattern inthe first portion, offset slightly). It will be noted that row 6 isoffset slightly from the position that it would have had had it been acontinuation of Set X.

Row 6, then, is the start of Set Y in which the helical,

angle of offset 'y for each succeeding row 7-10 is the same as thehelical angle of offset 7 for Set X but opposite in direction. Then anew row 1 starts a new Set X which is identical to said first Set X butdisplaced around the periphery of said disintegrating element 26 by 10rows of teeth tips 25. Sets of rows of different sizes from two to aboutten rows can be used with essentially equivalent results in that lateralfiber density migration is minimizedJThe size of the sets is a functionof the number of teeth 24 on each rotor 23 and the number of rotors 23in the disintegrating element 26.

For example, where two hundred and sixty-four rotors 23 having eightteeth 24 per rotor are used, it has been found satisfactory toarrangethe tips 25 in sixteen sets of five rows each, using a helicalangle of about 23. In such a case, each row would comprise aligned teeth24 on'every eleventh rotor 23. It will be recognized that once a singletooth 24 on a rotor 23 has been positioned, all of the other teeth 24 onthe same rotor 23 will be automatically positioned.

Some such arrangement of the teeth tips 25 is required to prevent thepattern of the teeth tips 25 from causing lateral migration of thefibers and to minimize noise and vibration reinforcement. The discloseddesign keeps a relatively constant distribution of fibers across the airflow channel 31 defined by the casing 16 and said disintegratingelement26.

The air flow channel 31 is defined by the disintegrating element 26 andthe casing 16 which'is sized to give from about 1/32 to about Mr inchclearance, preferably about 3/32 inch clearance between blade tips 25and the casing 16.

Avoidance of preferential lateral migration of fibers to one side or theother and the maintenance of a relatively even air velocity profileacross the width of the air flow channel 31 by the methods describedhereinafter are essential if one is to obtain'an airfelt having alaterally constant basis weight when the disintegrator 13 is closelycoupled as defined hereinafter.

The air inlet 21 can be a single slot-7a inch wide across the width ofthe casing 16 (typically about 16 inches) which under a pressure ofabout 2-l0 inches of water will deliver about 6,000 to about 13,000,preferably 8,000 feet per minute air velocity. This is the only airintroduced deliberately to the disintegrator 13.

It should be noted that part of the velocity imparted to the fibersdischarged through the discharge outlet 20 is obtained directly from theteeth 24; and accordingly, it is unnecessary to add large quantities ofair to maintain the velocity of the individual fibers through thedischarge outlet 20 when the disintegrator'13 is closely coupled asdefined hereinafter.

Referring now to FIG. 4, one can see a row of air inlets 22 having across-sectional area of aboutl square inch are desirably provided acrossthe discharge outlet 20 of the casing 16. When the air flow through eachof 5 for the purpose of forming an airfelt having a predeterminedvariation in basis weights across its width. Within the outlet 20 aredisposed a central diverting vane 32 and two side diverting vanes, 33and 34. These vanes 32, 33 and 34 vary the fiber density across thecross-sectionof the discharge outlet 20 by diverting extra fiber intothe other portions of the discharge outlet 20 to increase the fiberdensity in these portions. The primary fiber diverting surfaces 35, 36,37 and 38 andthe other surfaces of the vanes 32, 33 and 34 on whichfibers can impinge are all slanted a maximum of about 45, preferably nomore than about 25, from the line of air flow so as to divert the fibersinto the approximate centers of the adjacent open areas of the dischargeoutlet 20, without buildup of fibers on those surfaces. The vanes 32, 33and 34 can be solid, hollow, or simply one or more thin plates slantedso as to divert fibers to one'side or the other of the vanes 32, 33 and34.

The fiber impinging edges should either be rounded or slanted a maximumof about 45 from the line of air flow to avoid fiber buildup. The lengthand width of the vanes can be sized as required to produce a desiredcross-sectional variation of basis weight in .the airfelt product. FIG.6 shows a cross-section of the product of the arrangement of FIGS. 1 and5.

Referring now to FIG. 7, another preferred variation of this inventionshows a second pyrimidal vane 39 disposed against the wall of the casing16 to redivert fibers which may migrate back into the space in thedischarge outlet 20 directly below the first central diverting vaneabout 40 percent open with a paper tissue running on the individual airinlets 22 is adjusted to provide an air velocity of from about 6,000 toabout 13,000 fpm, preferably 8,000 fpm air velocity, by means of apiccolo valve, it is possible to control the direction of the highvelocity fiber/air mixture flowing through the discharge outlet 20 andthereby vary the fiber density across the axial width of the dischargeoutlet 20. The inlets may be slanted down or up, or be perpendicular tothe air flow, but are preferably slanted down about 30 from thehorizontal. These air inlets 22 provide fine tuning for adjusting thefiber deposition rate across the width of the outlet 20. When thedisintegrator 13 is close coupled as defined hereinafter, this permitsthe formation of a very even density airfelt. It is contemplated thateven rather extreme modifications of the air velocity profile can beaccomplished by using these air inlets 22.

top, the tissue having a basis weight of about 12 pounds per 3,000square feet.

It is a special advantage of the disintegrator of this invention thatdue to the tangential discharge outlet 20 and the relatively low volumeof air flow required, the disintegrator 13 can be close-coupled to thesupport element 40, Le, the distance from thecenter of saiddisintegrating element 26 to the support element 40 is from aboutthree-fourths of said disintegrating elements 26 diameter to about 2diameters, but with an absolute distance of no more thanabout 3 feet.Greater distances are less desirable since the residence time in thesystem becomes too great and the velocity of the fibers drops to anundesirable level. This close-coupling arrangement makes it possible tolay an even airfelt with very little air in the fiber/air mixture, thusminimizing the problem of passing the air through the support element40. Another advantage of close-coupling is the ability to start and stopthe associated converting line without changing the basis weight of theairfelt because of the minimal amount of fiber held up in the system atany time. Typically, fiber/air ratios (by weight) of from about 0.02 toabout 0.50, preferably from about 0.10 to about 0.40, are used.

Referring now to FIG. 8, it is preferred to provide certain vacuum airdischarge outlets 42, each having a cross-sectional area of about 9%square inch in the casproximately an inch away, and in the middle of theinlet opening 19 the air outlet holes 42 are'approximately two to fourinches away from the edge of the support element 19a. Although holes 42are shown only in the top portion of the casing 16 defining inletopening 19, it is desirable, and preferable, to provide similar holes 42in the bottom portion of the casing 16 defining inlet opening 19. Theholes 42 should not be too close to the airflow passage 31 or the flowof air into the outlet holes 42 may draw in fibers, but the air outletholes 42 should be sufficiently close to the edge of the support element19a so that any fibers which naturally migrate into the inlet opening 19will be removed. Otherwise, inlet opening 19 can become stopped andclogged with fibers preventing the sheet 12 from feeding into thedisintegrator. If desired, the fibers which are removed through theoutlet openings 42 can be conveyed to the support element 40 to helpform the airfelt.

More specifically, using the apparatus described hereinbefore, theprocess of this invention comprises disintegrating dried cellulosicfibrous sheet material in a process comprising the steps of:

A. Feeding the fibrous sheet 12 into the disintegrator B. Rotating thecylindrical disintegrating element 26 at a speed sufficient to move thetips 25 of the teeth 24 of the disintegrating element at a velocity offrom about 6,000 feet/minute to about 30,000 feet/minute, preferablyabout 15,500 feet/minute, whereby the tips 25 of the teeth 24 impactagainst the end of the fibrous sheet 12 to disintegrate the fibroussheet 12 into individual fibers;

C. Adjusting the amount of air flowing through the air inlets 21 tominimize recycling of the fibers;

D. Adjusting the amount of air flowing through secondary air inlets 22so as to achieve the desired fiber/air profile across the width of thedischarge outlet 20; p

E. Adjusting the air flow through vacuum air discharge outlets 42 toremove fibrous material which migrates into the space defined by thesupport element 19a and the sheet 12; and

F. Directing the fiber/air mixture from the disintegrator 13 through thedischarge outlet 20 and a' moving foraminous support 40, leaving thefibers on the foraminous support 40 in the form of an airfelt 41.

Referring to FIG. 1, when the sheet 12 is fed into the disintegrator 13through the slotted inlet opening in the inlet portion 19 at a rate ofabout 60 fpm., the inner end 19a provides a support for the sheet 12.The disintegrating element 26 rotating in a counterclockwise manner,disintegrates the sheet 12 when the tips 25 impact the sheet 12 at aspeed of at least 6,000 feet/minute, preferably about 15,500feet/minute. Individual fibers are then mixed with the air which isinserted through the air inlet 21 at the rate of about 8,000 fpm. Theair, which is inserted through the air inlet 21 prevents the rotation ofthe disintegrating element 26 from drawing air from the rest of thecavity within the disintegrator 1-3, i.e., it prevents recycling.

When the air in air flow channel 31 is mixed with th individual fibersat the point of impact of the tips 25 with the sheet 12, the resultingfiber/air mixture flowing through the channel 31 has a relatively evenvelocity distribution and consequently an even fiber density profileacross the width of the channel 31. It is at this point thatdisintegration to individual fibers is completed by the action of theteeth 24, the shearing and abrasion effects resultingfrom theinteraction between the blades and the casing, and the turbulence in therestricted channel 31. If such a restricted passageway is not provided,or if the channel 31 is too short, then disintegration is incomplete.This evenvelocity profile and fiber density profile is maintained sincethe pattern of the teeth 24 on the surface of the disintegrating element26 does not preferentially divert fibers to either side of the air flowchannel 31. Since the distance from the disintegrating element 26 to thesupport element 40 is very short and in a straight line, this fiberdensity profile does not havea chance to redistribute and accordingly,it is possible to lay a very even basis weight airfelt on the supportelement 40. If required, variations in the air flow velocity profile andfiber density profile can be made by adjusting the input of air throughthe individual air inlets 22. g

It is also possible to modify the basis weight distribution of theairfelt by means of the vanes 32, 33 and 34, and secondary diverterslike diverter 39. It should be noted that these vanes 32, 33 and 34 haveslanted edges and diverting surfaces 35, 36, 37 and 38 to divert thefibersrather than to simply stop the fibers. This avoids buildup offibers on the surfaces 35, 36, 37 and 38. Similarly, the diverter 39 hasslanting edges and surfaces to avoid fiber buildup. The diversion of thefibers builds up the other areas which are not underneath the vanes 32,33 and 34 at the same time that the fibers are being prevented fromdepositing on the area underneath the vanes 32, 33 and 34. Thus, theeffect of the vanes 32, 33 and '34 on the difference between basisweights of these adjacent areas is greater than the effect of the vanes32, 33 and 34 on the basis weight of the area directly under the vanes32, 33 and 34.

Another preferred embodiment of the invention involves the process ofkeeping the inlet opening 19 free of disintegrated fibers. This is doneby pulling a vacuum of from about l0 to about 40 inches of water on theholes 42, the vacuum being of sufficient strength to re-,

move those fibers migrating into the inlet 19, but preferably notsufficient to pull large amounts of additional fibers into said slottedinlet 19. It is desirable that the holes 42 in the middle of the slotinlet 19 be from about 2 to about 3 inches from the support element 19a.However, the holes 42 along the sides of the slot inlet 19 can be closerto the support element 19a, i.e., about an inch. Placing the holes 42 soclose to the support element 19a along the sides of the slot inlet 19may cause some fibers to migrate from the air flow channel 31 into theslot of the inlet portion 19; however, the need to remove fibers fromthe sides of the slot of the inlet portion 19 is sufficiently great tojustify drawing additional fibers in. Failure to remove the fibers fromthe slot of 1 1 v the inlet portion 19 results in a buildup of fiberswhich eventually will jam the slot of the inlet portion, 19. I What isclaimed is: 1. An apparatus for preparing an airfelt comprising:

A. A disintegrator for fibrous material comprising:

1. A rotary cylindrical disintegrating element rotat able about itscylindrical axis, said element having teeth generally randomly disposedon said disintegrating elements periphery with the impacting faces ofsaid teeth inclined inwardly in the direction of rotation at an .angleof from aboutlS to about 40 from the radii drawn through the front edgesof the teeth s tips and the top surfaces of said teeth being inclinedinwardly to form a relief angle of from about 20 to about 60; and

2; a casing for said disintegrating element comprising inlet meansdefining a support element for said fibrous material to support saidfibrous material while it is being fed into a position where saiddisintegrating element can impact the fibrous material to separate saidmaterial into its individual fibers, the distance between saiddisintegrating element and said support element being from about 0.010to about 0.080 in., said casing defining, in cooperation with saiddisintegrating element, a restricted air flow channel to keep thecurrent of air and entrapped individual fibers, which result fromrotating said disintegrating element to disintegrate said fibrousmaterial, within a minimal cross-sectional area, said casing having aprimary discharge outlet for the air and fiber current, said dischargeoutlet being tangentially directed with respect to said disintegratingelement, said casing having an air inletimmediately adjacent the saidprimary discharge outlet and between said primary discharge outlet andthe point wherethe fibrous material is impacted, said casing havingsecondary air inlets in the casing across the width of said primarydischarge outlet; and said casing having vacuum air outlets in saidinletmeans spaced upstream about 1- inch to about 4 inches from thepoint where the disintegrating element impacts said fibrous material;and

p B. A moving foraminous support element across the opening of saiddischarge outlet adapted to collect the individual fibers to form anairfelt while permitting the air to escape through said foraminoussupport element, said foraminous support element being at a distancefrom the center of said disintegrating element'of from aboutthree-fourths toabout two diameters of said disintegrating element butno further than about 3 feet.

2. The apparatus of claim 1 containing diverting vanes disposed in saidprimary discharge outlet, said vanes having impacting surfaces whichslant toward the outlet end of said primary discharge outlet, the degreeof slant measured from the line of air flow being a maximum of about 45whereby fibers are diverted away from the area beneath said vanes andinto adjacent areas without any appreciable buildup of fibers on saidsurfaces.

3. The apparatus of claim 2 wherein said degree of slant is no more thanabout 25.

4. The apparatus of claim 1 wherein said discharge outlet is from about5 to about 270 around the circumference of the casing in the directionof rotation of said disintegrating element from the point where saiddisintegrating element impacts said fibrous material.

1. An apparatus for preparing an airfelt comprising: A. A disintegratorfor fibrous material comprising:
 1. A rotary cylindrical disintegratingelement rotatable about its cylindrical axis, said element having teethgenerally randomly disposed on said disintegrating element''s peripherywith the impacting faces of said teeth inclined inwardly in thedirection of rotation at an angle of from about 15* to about 40* fromthe radii drawn through the front edges of the teeth''s tips and the topsurfaces of said teeth being inclined inwardly to form a relief angle offrom about 20* to about 60*; and
 2. a casing for said disintegratingelement comprising inlet means defining a support element for saidfibrous material to support said fibrous material while it is being fedinto a position where said disintegrating element can impact the fibrousmaterial to separate said material into its individual fibers, thedistance between said disintegrating element and said support elementbeing from about 0.010 to about 0.080 in., said casing defining, incooperation with said disintegrating element, a restricted air flowchannel to keep the current of air and entrapped individual fibers,which result from rotating said disintegrating element to disintegratesaid fibrous material, within a minimal crosssectional area, said casinghaving a primary discharge outlet for the air and fiber current, saiddischarge outlet being tangentially directed with respect to saiddisintegrating element, said casing having an air inlet immediatelyadjacent the said primary discharge outlet and between said primarydischarge outlet and the point where the fibrous material is impacted,said casing having secondary air inlets in the casing across the widthof said primary discharge outlet; and said casing having vacuum airoutlets in said inlet means spaced upstream about 1 inch to about 4inches from the point where the disintegrating element impacts saidfibrous material; and B. A moving foraminous support element across theopening of said discharge outlet adapted to collect the individualfibers to form an airfelt while permitting the air to escape throughsaid foraminous support element, said foraminous support element beingat a distance from the center of said disintegrating element of fromabout three-fourths to about two diameters of said disintegratingelement but no further than about 3 feet.
 2. a casing for saiddisintegrating element comprising inlet means defining a support elementfor said fibrous material to support said fibrous material while it isbeing fed into a position where said disintegrating element can impactthe fibrous material to separate said material into its individualfibers, the distance between said disintegrating element and saidsupport element being from about 0.010 to about 0.080 in., said casingdefining, in cooperation with said disintegrating element, a restrictedair flow channel to keep the current of air and entrapped individualfibers, which result from rotating said disintegrating element todisintegrate said fibrous material, within a minimal cross-sectionalarea, said casing having a primary discharge outlet for the air andfiber current, said discharge outlet being tangentially directed withrespect to said disintegrating element, said casing having an air inletimmediately adjacent the said primary discharge outlet and between saidprimary discharge outlet and the point where the fibrous material isimpacted, said casing having secondary air inlets in the casing acrossthe width of said primary discharge outlet; and said casing havingvacuum air outlets in said inlet means spaced upstream about 1 inch toabout 4 inches from the point where the disintegrating element impactssaid fibrous material; and B. A moving foraminous support element acrossthe opening of said discharge outlet adapted to collect the individualfibers to form an airfelt while permitting the air to escape throughsaid foraminous support element, said foraminous support element beingat a distance from the center of said disintegrating element of fromabout three-fourths to about two diameters of said disintegratingelement but no further than about 3 feet.
 2. The apparatus of claim 1containing diverting vanes disposed in said primary discharge outlet,said vanes having impacting surfaces which slant toward the outlet endof said primary discharge outlet, the degree of slant measured from theline of air flow being a maximum of about 45* whereby fibers arediverted away from the area beneath said vanes and into adjacent areaswithout any appreciable buildup of fibers on said surfaces.
 3. Theapparatus of claim 2 wherein said degree of slant is no more than about25*.
 4. The apparatus of claim 1 wherein said discharge outlet is fromabout 5* to about 270* around the circumference of the casing in thedirection of rotation of said disintegrating element from the pointwhere said disintegrating element impacts said fibrous material.